Message broadcast systems such as radio networks are well known. Message broadcast systems may be employed to convey information along a highway for radio reception in vehicles traveling therealong or for reception by series of electronic billboards therealong for viewing by travellers in vehicles. Message broadcast systems may also be employed in localized coverage areas such as an amusement park or other tourist attraction, to broadcast messages for reception in vehicles or for announcement over public address systems.
Known message broadcasting systems have heretofore been limited in terms of the number of different messages that can be broadcast in different areas of the system. Known message broadcast systems have also been limited in their ability to update or change the broadcast messages. For example, U.S. Pat. No. 4,742,530, to Kawai discloses a radio relay system including a repeater which is able to detect a desired signal from an unwanted signal. However, each transmitter in the Kawai system is a licensed radio transmitter. A large number of licensed transmitters are necessary, to broadcast a large number of distinct message sequences over different areas of the system. As is well known to those having skill in the art, licensed transmitters are expensive, and radio slots are of limited availability. Accordingly, the number of different message areas is severely limited.
Other message broadcast systems have been devised which employ low power unlicensed transmission. See for example U.S. Pat. No. 4,578,815 to Persinotti, which discloses a "simulcast" system of low power transmitters which are employed to transmit the same message over a wide area simultaneously. Unfortunately, while such a low power transmission system eliminates the problems of multiple licensed transmitters, this system can only broadcast the same message over a large area. The Persinotti system cannot transmit different messages to different portions of its coverage area. Moreover, the system must be disabled when a new message is added, a message is eliminated, or the sequence of messages is changed. For a highway or other vital information system, this down-time is unacceptable.
It is known to employ remote radio transmitter control for communication systems. See for example U.S. Pat. No. 4,481,671 to Matzold et al., in which a remote control for a remote transmitters transmits switching and control signals within the some frequency bands. However, there is no suggestion as to how this system might be used in a remotely controllable message broadcast system, which is capable of broadcasting different messages in different areas of coverage, and which may be programmed simply without down-time.
Finally, it is known to use recorders for continuous playback of messages. See for example U.S. Pat. No. 4,636,880 to Debell which describes a programmable annunciator for periodic fade-in of specific message segments in a continuous broadcast or background audio. It is also known to employ solid state digital recorders for recording and playback of messages. See for example U.S. Pat. No. 4,772,873 to Duncan in which a digital recorder can record low frequencies and high frequencies by changing the frequency of the clock source. However, there is no suggestion in either of these references to use a digital recorder for purposes of obtaining a versatile, remotely controllable message broadcast system. Moreover, there is no suggestion for using such a digital recorder in a system which permits messages to be changed without down-time.